The present invention relates to an extrusion device for extruding material from cartridges, having at least one plunger rod which can be moved.
Such extrusion devices are used in construction applications, for example, for extruding material from cartridges which are filled with silicone or other liquid and/or semiliquid construction materials. These cartridges typically have a cylindrical body with a discharge opening arranged on one end wall. The opposite end wall is formed by a male element which can travel inside the cylindrical body, such that the volume of the cartridge can be modified using the movement of this end wall, and as a result the contents of the cartridge can be pressed out through the discharge opening. The extrusion device enables an exact dosing as well as the precise application of the construction material. The extrusion device typically has a plunger which is arranged on a plunger rod, said plunger abutting the male element of the cartridge and being able to move the same toward the discharge opening for the purpose of extruding the material in the cartridge. The extrusion device also has an advancement device which can engage on the plunger rod and compel the same in a direction of advancement.
Conventional extrusion devices have a clamp element which can cant on the plunger rod. The clamp element is canted on the plunger rod, and then moved in the direction of advancement, whereby the plunger rod moves in an extrusion direction, and the material in the cartridge is accordingly extruded. However, these advancement devices have the disadvantage that it is only possible to extrude the material in the cartridge in a step-wise manner, because in order to change the position of the clamp element on the plunger rod, the advancement device must be completely disengaged each time.
In the prior art, for the purpose of enabling a continuous extrusion process, extrusion devices are known which have a traction mechanism which is attached on one end thereof to an end of the plunger rod. On the opposite end thereof, the traction mechanism is coiled around a spool. The spool is driven using a continuous drive, for example by an electric motor, such that it is possible to extrude the material in the cartridge in a constant manner. Such an advancement mechanism, however, has the disadvantage that the traction mechanism must be stowed inside the housing and takes up more space when fully rolled up around the spool. In addition, with this coiling method, due to the expanding radius around the spool produced by the coiled part of the traction mechanism, the advancement movement is accelerated in the direction of extrusion, thereby extruding more material. In configurations wherein the traction mechanism is coiled in coil paths which are adjacent to each other, undesired shear forces are exerted on the plunger rod due to the changing skew of the traction mechanism. These shear forces can lead to a canting or deformation of the plunger rod.